change color of output graph

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Anvinder Singh
Anvinder Singh 2016-3-2
评论： Anvinder Singh 2016-3-2
I have a matlab plot (draw rectangle using matrix) but it shows the output in blue color whereas i want it in black color. How can i change it to black color ?
a = ones(256, 256, 3);
a(10:110,40:140)=0;
a(120:200,120:200)=0;
image(a)
I want the intensity of each square to be different actually. One should have intensity 100 and the other to be 300.

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采纳的回答

Geoff Hayes
Geoff Hayes 2016-3-2
Anvinder - the problem is with the following two lines
a(10:110,40:140)=0;
a(120:200,120:200)=0;
Remember, a is a 256x256x3 matrix. In the above, you are only setting the Red component to zero. These two lines would be equivalent to
a(10:110,40:140,1)=0;
a(120:200,120:200,1)=0;
If you want the squares to be black, then you need to set all three components (red, green, and blue) to zero using
a(10:110,40:140,:)=0;
a(120:200,120:200,:)=0;
When I try the above, the pale blue squares are replaced with black ones.
  2 个评论
Anvinder Singh
Anvinder Singh 2016-3-2
Thanks Geoff, This is awesome. I didnt think about the third component at all. One more query, If i need to vary the intensity of the squares to some other grayscale value then should i do it by replacing '0' in the equation above or do something else ?
Geoff Hayes
Geoff Hayes 2016-3-2
Yes, Anvinder. Just use any value between 0 and 255.

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更多回答（2 个）

Image Analyst
Image Analyst 2016-3-2
You can use an indexed image if you don't want an RGB image and want values of 0, 100, and 300, and want the 100 and 300 both to show up as black. Just set up a colormap and apply it.
a = zeros(256, 256);
a(10:110,40:140) = 100;
a(120:200,120:200) = 300;
imshow(a, []);
cMap = [1,1,1;0,0,0]
colormap(cMap);
colorbar
caxis([0, 100]);
Muhammad Usman Saleem
编辑：Muhammad Usman Saleem 2016-3-2
Accept this answer if satisfy your question
try
plot(array1,array2,'k')%k stand for black color
for more reading,
http://www.mathworks.com/matlabcentral/answers/8558-plot-different-colors-while-using-loops
http://www.tutorialspoint.com/matlab/matlab_plotting.htm
  1 个评论
Anvinder Singh
Anvinder Singh 2016-3-2
plot(array1,array2,'k')%k stand for black color doesnt work for this plot. Why will i get blue plot in the first place when i give the value of the two rectangular matrices =0 ? Shouldnt it give a black rectangle ?
Is there a way to change the color of the rectangles i plot using matrix such that each rectangle can have different intensity..

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